Direct-voltage regulating circuit



Jan. 6, 1959 C. W. HARRISQN DIRECT-VOLTAGE REGULATING CIRCUIT Filed Deo. 27, 1955 k QN w ATTORNEY Dinner-vorraus nseurarmo cincurr 'Charles William Harrison, Millington, N. J., assignor to Harrison Laboratories, Inc., Berkeley Heights, N. I., a corporation of New Jersey This invention relates to an improved electronic directvoltage regulating circuit. n

An object of this invention is to provide nearly perfect regulation of a direct-voltage from no load to full load.

Another object is to providea relatively simple and inexpensive apparatus which can maintain a nearly perfect constant output voltage in spite of appreciable source resistance and changes in current drawn from the source and in spite of changes in power line voltage and of ageing of elements of the regulating apparatus itself.

A further object is `to provide a source of voltage which is stable and remains stable and which retains substantially its highest efficiency throughout a long and Voltage regulating circuits of various kinds areknown in the art and have been used for many years. Some of these circuits are elaborately designed and made very complicated in an effort to provide perfect voltage regulation. Unfortunately, though, many of these circuits because of their own complexity sometimes fail to achieve their purpose becauseof hidden faults such as frequent part failure due to complexity, overloading or unstability brought on by ageing of critical parts. lven though in fact some of these circuits are reliable and do give what amounts to perfectvoltage regulation under severe operating conditions, they are far too costly and too bulky to even be considered for commercial applications, and hence remain only laboratory Curiosities.

On'the other hand, simple voltage regulating circuits have been developed in the past but these almost invariably sacrifice regulating efficiency or stability to the point where none of these circuits is suitable for use vin critical commercial applications, such as in radio broadcasting installations.

The present invention is intended to overcome the.

above outlined drawbacks of prior art voltage regulators.

In accordance with a specific embodiment of the present invent1on, an output direct voltage is electronically measured against a known reference voltage to obtain as a control signal the difference, if any, between the output.

and the reference voltages. This control signal is then ampliedand applied to a variable electronic resistance in series with the output voltage vlead land a source of unregulated direct voltage. This control signalis obtained and amplified in a unique and greatlyv improved circuit, though the signal controls a previously known variable electronic resistance in the usual Way. The circuit by which the control signal is derived is designed so that, though surprisingly few parts are used,

theoutput voltage of the overall apparatus is substancharacteristics` of the electron tubes used in the circuit.

Moreover, this output'voltage is substantially independent of current even though very heavy current is drawn from the apparatus and even though the unregulated voltage applied to the circuit is greatly affected by changes in current.

` In an actual model of the invention which has been built and tested, an output voltage of 285. voltswas regulated to within 0.01 volt as the current drawn from the apparatus was increased from zero to 1500 milliamperes. Apart from the tubes comprising the variable electronic resistance, a singlegenvelope double triode, a singley envelope triode-pentode, anda single voltagek regulating tube were the only tubes required in the circuit. A correspondingly small number of resistors and capacitors sufced. The entire apparatus including the electronic ,resistance tubes was built on a chassis four by eight and three-quarters by fourteen inches and weighed only ten pounds. f

ln tests made on this model of the invention it appears that the output voltage is not only substantially independent of the unregulated input voltage, but is, also substantially independent of minor manufacturing differences in the control tubes, of changes in the filament voltages of these tubes, and of changesin the tube characteristics due to ageing. The transient response of the apparatus to sudden changes in load is excellent 'and shows that the controly circuit is lvery stable.

A better understanding o f the invention together with a fuller appreciation of its many advantages will best` be gained from a study of the following description. This description is given in connectionl with thev single ligure of the drawing showing a schematic diagram of a circuit embodying features of the invention.

The circuit 10 shown in thissingle figure is supplied at the left via lead 12 with an unregulated positive vdirect voltage from a source not shown. `A large filter capacitor i3, connected between lead l2 and ground eliminates any sudden surges in the voltage on lead 12. This volitage is connected to lead' lst/through the variablek electronic resistance generally indicated at lr6. This electronic resistance includes aplurality of ktriodes i8; connected in parallel and havingv grid isolating resistors 22, and

` tially independent of' variations, within a range, in the cathode bias resistors 24 respectively. These `triodes 18 are grid controlled, through av variable voltage applied to the lead 26, and act in the well known Way tOkkCep the direct voltage on lead. 14 substantially constant. There should be used as many triodes i8 as required; to

`handle the current drawn'fromV circuit lil. They are protected from overloading by the. rectifier,l Zwhich-is connected between leads 26 andV 14 and isy poled toiprevent lead 26 becoming more positive than lead 14. This, according to the known operation of clipping amplifiers, such as in the voltage limiters of F.,M. receivers, prevents the triodes i8 from conducting more current than allowed by cathoderesistors 24 when the lead 26Vis connected directly to lead 14. n

Connected near, tne right end of lead i4 are the series resistors 3i), 3l and 32. Resistor 3l is variable and its slidable tap is connected to` the grid lead 34 of the direct voltage amplifier triode 3o. This tube is cathode coupled through the common c'a'thode'resistorr 38 to the reference voltage triode arnplif1er4tl. v The plate of tube` 36 is supplied directly from lead l@ with positive voltagefand the 'plate of tube lll is supplied through the plate resistor 44.

. Patented Jan". 6, 1959 Thus as the tubes age, resultingin i 'about four is satisfactory.

other things being unchanged, once the voltage on lead `14 is set at a value, by moving the tap on resistor 31, the

voltage will remain substantially at this value even though the characteristics of tubes 36 and 40 change slightly.

vAs mentioned, tubes 36 and 40 areconnected so that the voltage at plate lead 46 is dependent on the voltages f applied to the grids of these two tubes. grid lead 34 is normally negative relative to the cathode .and is directly proportional to the voltage on lead 14.

The voltage on The voltage on the grid lead 48 of tube 40 is also negav tive to cathode and is substantially completely iii-dependent of the voltage on lead 14, being kept independent by the gas discharge voltage regulating tube 50. This tube `is energized from lead 14 by the dropping resistor 52 and is connected to the Vgrid of triode 40 by the resistor e 54. A'liltering capacitor S6 is also connected to this grid g to keep any significant voltage transients from reaching it. Since lead 14 is maintained atnearly exactly constant vfvoltage, regulator tube 50 will draw nearly constant current and consequently will maintain a more nearly coni. stant discharge or glow voltage. This discharge voltage is the reference against which the voltage on lead 14 is measured and with which the latter is compared. Any

variation between the two is detected by tubes 36 and 40 'and then amplified and applied to lead 46.

To increase the normal gain from grid lead 34 to plate lead 46 through tubes 36 and 40, a resistor 58 is connected between these two leads.- The size of this resistor is such that the gain of tubes 36, 40 at zero frequency is increased to upwards of four times the gain without "difference in the nearly perfect constancy of regulation of the voltage on lead 14 and without causing unstability of the circuit. This fact is an important advantage of the invention.

-In actual practice, the use of an increase in gain of This also makes possible somewhat easier servicing of the circuit because tubes 36 and 40 with a gain increase of four are stable when The output voltage from tubes 36 and 40 is directly connected via the plate lead 46 to the control grid of a `pentode amplifier tube 62. The cathode of this tube is normally biased positive relative to the grid by the cathode resistor 64 which is also in common with the cathode of the triode 66. Thel plate of pentode 62 is energized through a portion of lead 26 and through the plate resistor 68 which is connected to input lead 12. The voltage drop across resistor 68 holds the grids of tubes 18 normally negative relative to their cathodes and at a value that provides the proper output voltage. The current conduction through pentode 62 controls this voltage drop, hence the current flow through tubes 18 and ultimately the voltage on lead 14.

The screen grid of pentode 62 and the plate of tube 66 are connected via the common lead 70 to lead 14 and are thus maintained at a constant voltage. Proper cathode bias for tube 62 is provided by tube 66 which is suitably biased through the series resistors 72, 74 and 76 connected between lead 70 and ground. -The grid of Itube 66 is connected to the junction of resistors 74 and 76 and is connected to ground through a filter capacitor` 80. Voltage from the plate of tube 62 is applied via the resistor 82 to the junction of resistors 72 and 74 and y thence to the grid of tube 66. The size of resistor 82 is chosen so that the gain of tube 62 is, as with tubes 36 and 40, increased by upwards of four times. Capacitor cuts off the high frequency regenerative signal fed from the plate of tube 62 via resistors 82 and 74 in much the same manner as capacitance 60 of the previous stage. By virtue of this arrangement, the cathode of tube 62 is properly biased without'using a second regulator tube such as tube 50. This decreases cost and also eliminates any diliiculties which might arise by having two separate reference voltages in the circuit. Moreover, and perhaps more importantly the regulating action of the circuit is further enhanced by the positive feedback provided by resistor 82 without danger of instability.

The output voltage of circuit 10 is obtained from lead 14 at output terminal 61 through the filter circuit generally indicated at 83. Also connected to terminal 61 is a large filter capacitor 86 which helps keep the voltage on this lead from changing suddenly.

The function of filter 83 is to make the regulator loop gain of circuit 10, including capacitor 60, and tubes 36, 40, 62 and 66, at frequencies above zero more nearly the same for no load and for full load. By so equalizing this gain, the transient stability of the circuit is improved and made more nearly independent of load. Filter' 83 corii sists of the inductor 88 having negligible resistance, the resistor 90, and the capacitor 92. The sizes of inductor 38 and resistor 90 depend on the difference in regulator loop gain between no-load and full-load outputs.

In a circuit substantially identical to that illustrated herein and which has been built and tested, thewcircuit elements and their values were as follows: capacitor 13, micro-farads; tubes 18, type Chatham 6336 (five of these double tubes used); resistors 22, 560 ohms each; resistors 24, 39 ohms each; diode 28, a silicon junction diode; resistor 30, 390,000 ohms; variable resistor 31, 25.000 ohms; resistor 32, 150,000 ohms; tubes 36, 40, a single 12AX7; resistor 38, 130,000 ohms; resistor 44, 240,000 ohms; tube 50, type 5651; resistor 52, 100,000 ohms; resistor 54, 10,000 ohms; capacitor 56, 0.01 microfarad; resistor 58, 4.7 meg-ohms; capacitor 60,0.1 microfarad', tubes 62, 66, a single type 6AN8; resistor 64, 22,000 ohms; resistor 68, 240,000 ohms; resistors 72, 74, 51,000 ohms each; resistor 76, 180,000 ohms; capacitor 80, 0.01 micro-farad; resistor 82, 3.0'meg-ohms; capacitor 8,6, 125 micro-farads; inductor 88, 300 micro-henries; resistor 90, 127 ohms; and capacitor 92, 2,000 micromicro-farads. The voltage applied to lead 12 was 395 volts at no-load and 375 volts at full load; the voltage at terminal 61 was 285 volts and changed leses than 0.01 volt as current drawn was increased from zero to 1,500 milliamperes.

The above description of the invention is intended in illustration and not in limitation thereof. Various changes or modifications may occur to those skilled in the art and these can be made without departing from the spirit or scope of the invention as set forth.

I claim:

1. In a high eiciency, high current capacity voltage regulating circuit, means including an input lead to supply an unregulated direct voltage, a variable electronic resistance connected between said input lead and a direct voltage output lead and adapted to be changed in resistance to keep the voltage on said output lead substantially constant, and control means connected between said output lead and said electronic resistance and including a first stage and a second stage, said first stage comprising first and second three electrode amplifiers matched and balanced to each other and having positive feedback which increases zero frequency gain by at least four times, the control electrode of one of said amplifiers being direct voltage connected to said output lead, the control electrode vof said other amplifier being connected to an independent reference voltage source, said second stage comprising a voltage amplifier Whose input is connected to the output of said rst stage fs and whose output is connected to said electronic resistance, said second stage voltage amplifier also having positive feedback which increases zero frequency gain by at least four times.

2. The combination of elements as in claim 1 inwhicn said second stage includes a pentode amplifier and a triode amplifier having a common cathode resistor, the plate voltage of said pentode being connected to control said electronic resistance and to control the grid of said triode, the grid of said pentode being connected to the output of said first stage.

3. In a voltage regulator, a feedback loop adapted to maintain a constant direct voltage on an output lead and including a first and a second voltage amplifier and an electronic variable resistance controlled by the output of said second amplifier and connected between said output lead and an input lead, said first amplifier including a first and a second three electrode tube the grid of the first being biased above ground through a dropping resistor connected between said o-uput lead and ground, the grid of the second being kept at an independent and constant potential, the cathodes of said tubes being biased relative to grid potential by a common cathode resistor, the plate of each tube being energized independently from said output lead, the plate of said second tube being connected to the grid of the first by means which increases zero frequency gain by at least about four times, said second amplifier including a third and a fourth tube each having a cathode, a plate and a grid, the grid of said third tube being connected to the plate of the second tube lof said first stage, the cathodes of said third and fourth tubes being connected to a common cathode resistor, the plate of said third tube being energized through a plate `resistor connected t-o said input voltage lead which has a potential higher than that of said output lead, the plate of said third tube being connected to the control element of said variable electronic resistance, the grid of said fourth tube being biased from said output lead.

4. The combination of elements as in claim 3 in which the grid of said fourth tube is connected to the plate of. said third tube by means which increases the zero frequency gain of said third tube by at least four times.

5. The combination of elements as in claim 3 in which said means which increases zero frequency gain includes a resistor connected between 'the grid of said first tube and said output lead and in which the grid of said first tube is capacitively bypassed, whereby the noload and full-load gains of said feedback loop are equalized and the transient stability of said regulator is improved.

6. The combination of elements as in claim 3 in further combination with a gas discharge regulating tube connected to the grid of said second tube whereby said grid is maintained at a substantially independent and exactly constant voltage.

7. The combination of elements as in claim 3 in which the plate of said fourth tube is energized from said output lead and said third tube has a screen grid which is energized from said output lead.

8. In a voltage regulator, a feedback loop adapted to maintain a constant direct voltage on an output lead and including a first and a second voltage amplifier and an electronic variable resistance controlled by the output of said second amplifier and connected between said output lead and an input lead, said first amplifier including a first and a seco-nd three electrode tube the grid of the first being biased above ground through a dropping resistor connected between said output lead and ground,

the grid of the second being kept at an independent and constant potential, the cathodes of said tubes being biased relative to grid potential by a common cathode resistor7 the plate of each tube being energized independently from said output lead, said second amplifier including a third and a fourth tube each having a grid, a plate and a cathode, thegrid of said third tube `being connected to the plate of the second tube of said first stage, the cathodes of said third and fourth tubes being connected to a common cathode resistor, the plate of said third tube being energized through a plate resistor connected to said input voltage lead which has a potential' higher 'than that of said output lead, the plate of said third tube being connected to the control element of said variable electronic resistance, the grid of said fourth tube being biased from said output lead, and being connected to the plate of said third tube by means which increases the -zero frequency gain o-f said third tube by at least four times.

9. In a voltage regulating circuit, a feedback loop adapted to maintain a constant direct voltage on an intermediate output lead and including a first and a second voltage amplifier and an electronic variable resistance controlled by the output of said second amplifier and connected between said intermediate output lead and an input lead, the direct voltage input of said first amplifier being connected to said intermediate output lead, an output terminal adapted to be connected to a load having a resistive component, and an equalizing filter connected between said intermediate output lead and said output terminal and including an inductor of negligible resistance and a resistor connected in parallel, said inductor and resistor having values which equalize the loop gain of said circuit at frequencies substantially above zero for no-load and for full-load, and a capacitor connected between said output terminal and the direct voltage input of said first amplifier whereby the transient stability of said circuit is improved.

10. The combination of elements as in claim 9 in further combination with a large capacitor connected between said output terminal and ground, and a small capacitor connected in parallel with said inductor.

11. In a high efficiency, high current capacity voltage regulating circuit, means including an input lead to supply an unregulated direct voltage, an output voltage lead, a variable electronic voltage-dropping element having a control terminal and being connected between said input lead and said output lead and a-dapted to be controlled to keep the direct voltage on said output lead substantially constant, and control means connected between said output lead and the control terminal of said variable element and including a first stage and a seco-nd stage of amplification, sai-d stages being direct current connected together, said first stage being direct current connected to said output lead, said second stage being direct current connected to the control terminal of said variable element, first feedback means direct current connected internally of said first stage to substantially increase the gain thereof, at very low frequenies only, and seco-nd feedback means direct current connected internally of said second stage to substantially increase the gain thereof at up to relatively high frequencies, whereby even though the gain of said stages is greatly increased by positive feedback, the effect of variations in the overall gain of said stages due to ageing, deterioratio-n and the like will be minimized and said circuit will be more nearly perfectly stable, and the output hum will be minimized.

l2. In a high efficiency, high current capacity voltage regulating circuit, means including an input lead to supply an unregulated direct voltage, a variable electronic resistance connected between said input lead and a direct voltage output lead and adapted to be changed in resistance to keep the voltage on said output lead substantially constant, and control means connected between said output lead and said electronic resistance and including a first stage and a second stage, said first stage comprising first and second three electrode amplifiers, a resistance potentiometer connected between a reference point of potential and said output lead and to the control electrode of said first amplifier to apply thereto a portion only of the voltage on said output lead, resistor means connected for positive feedback from said second the size of said bypass capacitor being sufficient to preyent hurn pickup and instability at frequencies higher than zero, the control electrode of said second amplifier p being connected to an independent reference voltage zsource, said second stage comprising another voltage arnplier Whose input is connected te the output of said rst stage and whose output is connected to said electronic resistance, said second stage being connected by positive v8 feedback means which increases its zero and higher fre quency gain substantially, whereby at frequencies above zero the stability of regulation of the circuit is improved by the connection of said bypass capacitor, but output hum is minimized.

References Cited in the le of this patent UNITED STATES PATENTS 10 2,443,541 Neustadt June 15, 1948 2,594,006 Friend Apr. 22, 1952 2,782,361 Baker Feb. 19, 1957 

